How to do a repair from bootup

[Daave]

Thank you for your information.
Yes, I cannot find the second 'R' option, so I think as you said may
need to do a registry repair.

Questions:
1) If I copied the 'system' file from 'repair' directory into the
'config' directory, does it harm to run the 'scannow' as suggested by
one guru?

I doubt there would be any harm. But there is never an absolute
guarantee.

2) What actually the 'system' file does?

That's the hive in the registry with all the system settings. The
(operating) "system" is Windows XP.

3) I think my XP always has a problem the boot problem from time to
time. This is the second time I installed my XP, my first
installation happened reboot problem from time to time and finally
cannot be rebooted. And now it seems the same problem.
Any idea why the registry get corrupted?

Bad software (cold be legit or malware) or hardware problems.

Actually, since you have had problems for a long time, if I were you, I
would just perform a clean install:

http://www.michaelstevenstech.com/cleanxpinstall.html

Another option is to perform hardware diagnostics:

http://www.elephantboycomputers.com/page2.html#Hardware_Tshoot

Assuming there is data on your hard drive that you don't want to lose,
you could remove the drive and either put in another PC as a slave or
put it an external USB enclosure so that you may have access to the
data. You could also purchase a new hard drive for your PC and *then*
perform the clean install (then you could always copy the data back from
your old drive). You may even want to consider purchasing a new PC
altogether. It depends on how much time and money you want to spend.

Of course, you could always try the Recovery Console method to try to
salvage your system. And if you succeed, then that's great. Still, I
would make sure you save your data from your hard drive first to be on
the safe side.